The invention relates to a method for the manufacture of interlocking parts, by both powder injection molding and by extrusion, and, more particularly, to a method of making double-layered metal parts in which at least one part is made by a powder metal extrusion method.
The methods of manufacturing parts by powder injection molding and by extrusion are well known. While the latter method is used only in combination with powdered metal for the extrusion of shaped metal parts, powder injection molding is used to manufacture both metal and ceramic parts. The method steps are largely identical. Thus, for example, the powdered metal is mixed with the desired alloying additives, also in powder form. This powder mixture thus formed is plasticized in a heated kneader with a polymeric organic binder (waxes and plastics) and subsequently granulated by processing in conventional injection molding machines. An injection molding tool similar to a plastics injection molding tool is used as the mold.
The injection-molded shaped bodies (green parts) are placed in a binder-removing furnace to remove and eliminate the binder. During the binder-removing process the molecule chains of the binder disintegrate as a result of thermal or chemical decomposition. At the same time, presintering of the metallic shaped bodies takes place, which imparts an adequate stability to the shaped bodies.
During sintering, which can be performed in vacuo or under a protective gas, the final material properties are imparted to the metallic injection-molded parts. Their density increases considerably and their dimensions shrink by up to 20%. Because of the considerable contraction, it has not previously been possible to manufacture interlocking parts by powder injection molding nor to manufacture double-layer shaped metal parts by a continuous extrusion process.